Method and apparatus for changing single drill pipe strings to



Sept. 20. 1966 J. G. JACKSON ETAL 3, 73,660

METHOD AND APPARATUS FOR CHANGING SINGLE DRILL PIPE STRINGS TO DUAL DRILL PIPE STRINGS Filed Oct. :50, 1963 2 Sheets-Sheet 1 R W L. E I Wmm m s 3 M 2 aa M Q Q m 3 w W t N 2 GE I. L II N m r .1 @m I i I! 1 ll I- l Xi 7 m H R MN 11m w L. t f 9 8 9 3 8 3 3 2 33 3% a .52

Y /aw 5M m1 g ATTORNEYS p 20, 1966 J. G. JACKSON ETAL 3, 73,650

METHOD AND APPARATUS FOR CHANGING SINGLE DRILL PIPE STRINGS TO DUAL DRILL PIPE STRINGS Filed Oct. 50, 1965 2 Sheets-Sheet 2 INVENTOR. JOHN G. JACKSON mgIHARLES O. VAIL ATTORNEYS United States Patent METHOD AND APPARATUS FOR CHANGING SINGLE DRILL PIPE STRINGS T0 DUAL DRILL PIPE STRINGS John Gordon Jackson and Charles 0. Vail, Denver, Colo., assignors to Gas Drilling Services Co., Los Angeles, Calif., a partnership Filed Oct. 30, 1963, Ser. No. 320,088 14 Claims. (Cl. 17557) This invention relates to equipment for the drilling of wells employing a dual pipe or drill string, and particularly to a method and means for installing an inner pipe string in a conventional single pipe string.

Such dual pipe strings include an inner pipe string so that a high velocity stream of fluid can be passed downwardly to a drill bit through an outer concentric passage to cool the bit, entrain the drill cuttings and carry them upwardly through an inner concentric passage to the ground surface and out of the bore hole. Prior art methods for converting to dual drill pipe strings suffer from various disadvantages. For example, the joints of the conventional single drill pipe string are limited to very close tolerances and thus some of the prior art methods for installing an inner pipe string inside the conventional single pipe string adversely affect the close tolerances of the joints of the conventional single drill pipe string, Also, some of these prior art methods involve the permanent attachment of machined members at one end of each section of the conventional drill pipe. These prior art methods and means necessitate the use of costly machine labor, equipment and tools. Furthermore, once the dual pipe string is made up by prior art methods, it often cannot be disconnected into its original form, but is handled and stored as assembled units. These disadvantages of the prior art methods and means for converting single pipe strings to dual pipe strings seriously aifect the economy and flexibility of the dual pipe strings produced thereby.

Accordingly, it is an important object of this invention to provide a method and means for reversibly converting conventional single drill pipe strings to dual drill pipe strings so that, when desired, the resulting dual drill pipe string can be completely disconnected into its original form for handling and storing.

Another object of this invention is to provide such a method and means which does not destroy the close tolerances of the joints of the original conventional single drill pipe string and yet a truly operable and eflicient dual pipe string is provided.

Still another object of this invent-ion is to provide such a method and means which does not involve the permanent attachment of machined members to each section of the original conventional drill pipe and does not involve the use of highly skilled labor or costly equipment.

A further object of this invention is to provide a method and means for converting any conventional single drill pipe strings to dual drill pipe strings speedily, efliciently and economically at the drilling location by the use of workers skilled in the art, ordinary hand tools and auxiliary services generally available at the drilling site.

Additional objects of the invention will become apparent from the following description, which is given primarily for purposes of illustration, and not limitation.

Stated in general terms, the objects of this invention are attained by providing a method and means which comprises introducing a first inner pipe section into a first outer, or conventional pipe section, said conventional pipe section having attached at the lower end thereof a drill bit for drilling with fluid pressure and an attachment means for connecting in flow relationship the lower end of the inner pipe section to the drill bit. A first coupling device is detachably or reversibly mounted on the upper .end of the first inner pipe section.

3,273,660 Patented Sept. 20, 1966 "ice The first coupling device, or coupling unit, being reversible, is not permanently fixed or attached, but can be completely disassembled from the pipe sections. The first coupling device serves the function of generating, through the efforts of skilled workmen with the aid of ordinary hand tools and auxiliary services, frictional forces upon both the upper end of the first inner pipe section and the upper end of the first conventional pipe section. These generated frictional forces are of a magnitude suflicient to maintain the desired radially spaced and longitudinal relationship between the inner pipe section and conventional pipe section in the assembled dual pipe section throughout the drilling process, and as will become apparent the coupling devices serve to seal the power or drilling fluid with-in the common outer and inner passages by sealing means on each coupling device.

Of course, the eventual dual pipe string is assembled at the surface similar to the single string and in like manner lowered into the bore hole, namely a second outer, or conventional pipe section is threadedly connected to the first conventional pipe section in the usual manner at the well head. In assembling the second section of the dual string at the surface, a second inner pipe section. is introduced into the second conventional outer pipe section so that the lower end of the second inner pipe section may eventually slip into sealing and coupling engagement with the first coupling device on the upper end of the first inner pipe section. A second coupling device or unit, identical to the first coupling device and thus interchangeable therewith, is reversibly mounted on the upper end of the second inner pipe section. The second coupling unit, as in the case of the first coupling unit, is made to generate frictional forces upon both the upper end of the second inner pipe section and the upper end of the second conventional outer pipe section to form a second assembled dual pipe section, as described hereinabove with respect to forming the first assembled dual pipe section. This process is repeated until the necessary number of dual string sections are assembled as a result of converting from single string sections and the drill string is formed in use in a manner identical to single string practice to permit drilling to the desired depth. The coupling units seal the joints between successive inner pipe sections and position the inner pipe sections concentrically but in spaced relationship within the respective conventional outer pipe sections of each dual pipe section.

The dual pipe string is disassembled by reversing the assembly process described above. In other words, each dual string section is separated at or adjacent the surface by disconnecting the outer pipes as would be done in disassembling a single string and then the individual dual sections are disassembled whereby the inner pipe is removed from the outer pipe with said outer pipe being reusable in a single or dual string. In carrying out the latter, the frictional forces generated in the coupling unit of each section are released, and the inner pipe section is removed from the outer conventional pipe section. All assembled dual pipe sections are thus compeltely disassembled and the coupling units and pipe sections are stored for future reuse:

A more detailed description of a specific and preferred embodiment of the invention is given below with reference to the accompanying drawings, wherein:

FIGURE 1 is a partial, longitudinal view, with portions broken out, partially in section, showing a converted dual drill pipe string;

FIGURE 2 is a vertical sectional view showing details of a coupling unit employed in the dual drill pipe string of FIGURE 1;

FIGURE 3 is a vertical sectional view showing an inserting tool used for inserting the coupling unit of 3 FIGURE 2 in the upper end of a conventional pipe section;

FIGURE 4 is a cross-sectional view taken along line 4-4 of FIGURE 3; and

FIGURE 5 is a cross-sectional view taken along line 55 of FIGURE 3.

A drill bit of the concentric type is provided with an upstanding tubular member or socket 11 adapted to receive in sealed relationship the lower end of the first inner pipe section 12. Drill bit 10 is threadedly engaged on the lower end of first conventional outer pipe section 13. Outer concentric passage 14 communicates with the interior of pipe section 12 through openings 15 and central passage 16 in bit 10. Thus power fluid, such as drilling gas, can flow downwardly through outer concentric, or annular, passage 14 of bit 10 through openings 15, suspend drill cuttings in the fluid stream, and carry them upwardly inside inner pipe section 12 through central passage 16, all in accordance with standard practice in the dual drilling string art.

Now, assuming that at the surface outer section 13 is connected to bit 10, the following will describe the operation of assembling by the present invention two dual pipe sections, it being understood that the necessary number are so assembled. Thereafter, the final assembly of the drill string follows precisely the conventional practice using conventional methods of joining and lowering into the well bore. A coupling unit 18 is mounted on the upper end of the inner pipe section 12 inside the upperend of the first conventional pipe section 13 and the size of the inner section 12 will result in the latter, after securement to section 13, being positioned substantially as in FIGURE 1 in sealed relationship with socket 11. This is accomplished with the aid of an inserting tool 19, shown in FIGURE 3, as described below, following a description of the coupling unit 18, best shown in FIGURE 2.

Each coupling unit 18 includes three elongate, resilient or elastic gripping members or fingers 21 made of preferably rubber or synthetis elastomeric material, it being understood that the number is only exemplary. The lower ends of fingers 21 are fixed to lower clamps 22 by means 23 embedded in the fingers and engaged in the lower clamps as shown. Other suitable methods of fastening fingers 21 to lower clamps 22 can, of course, be used. The upper ends of fingers 21 are similarly fixed to upper clamps 24 by screws 26 embedded in the fingers and threadedly engaged in the upper clamps. Lower clamps 22 are fastened to a lower guide ring 27 by screws 28 and upper clamps 24 are fastened to a coupling tube 29 by Screws 31.

Coupling tube 29 is provided with an internal, annular flange 32 formed by a snap ring or other means. Annular flange 32 is adapted to provide a locating means for the inner pipes and to insure that the ends of the inner pipes never pass same and thus flange 32 forms a limiting stop although such is rarely used for this purpose in actual operation. Two spaced seal rings 33 and 34 are mounted in spaced annular grooves 36 and 37, respectively, below flange 32, and two spaced seal rings 38 and 39 are similarly mounted in spaced annular grooves 41 and 42, respectively, above flange 32. Seal rings 33, 34, 38 and 39 are adapted for sealing the upper and lower ends of inner pipe sections from concentric passage 14, when inserted in coupling unit 18 both below and above flange 32, respectively.

Coupling unit 18, as mentioned hereinabove, is mounted on the upper end of the first inner pipe section 12, inside the upper end of the first conventional pipe section 13. This is accomplished by mounting coupling unit 18 in inserting tool 19, as shown in FIGURE 3. Compression arms 43 are made to engage on lower guide ring 27 and tension arms 44 are hooked on the lower end of coupling tube 29. By properly setting valve 46, air pressure is admitted to the top of piston 47 in cylinder 48, while the bottom of the cylinder, below the piston, is open to exhaust to the atmosphere. This causes pison 47 to move downwardly, and to urge compression arms 43 downwardly. The downward urging of compression arms 43 stretches fingers 21. Coil spring 17 holds tension arms 44 out and cam 20 operating on collar 25 forces tension arms 44 inwardly so they hook the lower end of coupling tube 29 on the up-stroke.

The stretching of fingers 21 reduces their thickness. The resulting reduction of the thickness of fingers 21 permits the simultaneous insertion of fingers 21 inside the upper end of the first conventional pipe section 13 and around and in embracing relationship the upper end of the first inner pipe section 12, as shown in FIGURE 1. After fingers 21 are thus inserted, they fit in slip fit fashion around the outside wall of the upper end of the first inner pipe section 12 and against the inside wall of the upper end of the first conventional pipe section 13. At this stage, valve 46 is set for shutting off the air pressure to the top of piston 47 and for exhausting both ends of cylinder 48 to the atmosphere. This releases the tension on fingers 21 so that they tend to return to their original, greater thickness. In so doing, fingers 21 expand and exert pressure, due to their elastic properties and compression, upon the outside wall of the upper end of first inner pipe section 12 and upon the inside wall of the upper end of first conventional pipe section 13, as shown in FIGURE 1.

The resulting pressure generated by compressed fingers 21 develops sufliciently great frictional forces upon pipe sections 12 and 13 to securely position the upper ends of pipe sections 12 and 13 radially, concentrically and longitudinally during the earth bore hole drilling process to follow. This completes the first dual pipe section, and the second conventional pipe section is assembled for eventual conection with the first conventional pipe section,13 in the conventional manner, as indicated at 51 in FIGURE 1. In carrying out the latter, it will be observed that seal rings 33, 34 and 38, 39 seal the ends of inner pipe sections 12 and 52, which are located adjacent flange 32, against leakage from concentric passage 14. At'the surface, a second coupling unit 53, substantially identical with coupling unit 18, is mounted on the upper end of second inner pipe section 52 inside the upper end of second conventional pipe section 49, with the aid of inserting tool 19, substantially as described hereinabove in connection with mounting coupling unit 18. This completes the second dual pipe section and the inner pipe 52 would be located approximately as shown in FIGURE 1 whereby when the second dual string is connected to the first, the lower end of pipe 52 should appear about as in FIGURE 2.

Additional dual pipe sections are made up in a similar way and the dual drill pipe string is made up with these sections in a manner comparable to joining sections of a single drill string. It will be understood that although inserting tool 19 has been shown and described in connection with the method and means of the invention, any

other similar, suitable inserting tool can be used for assembling the dual drill pipe string, or for disassembling it. The dual drill pipe string is disassembled by reversing the method described hereinabove for assembling it. Assuming that dual string sections have been disconnected with a plurality of sections being at the surface, the top coupling unit of one section, such as coupling unit 53, is fitted with inserting tool 19 and fingers 21 are stretched, as described above. As previously indicated, fingers 21 can be stretched by pulling upwardly on tension arms 44 by adjusting valve 46 so that air pressure is admitted to the top of piston 47 in cylinder 48. The stretching of fingers 21 removes their compressive forces and coupling unit 53 is lifted out of or removed from the upper end of the upper conventional pipe section, such as section 49. The upper, inner pipe section, such as section 52 is lifted out of or removed from the upper conventional pipe section, such as section 49. The resulting, disassembled, conventional outer pipe sections, inner pipe sections and coupling units are stored for reuse With the outer pipe sections being reusable in single pipe drill strings.

Although the use of fingers 21 was described in detail in the specific embodiment of the invention illustrated and described hereinabove, it will be understood that various other gripping members can be used in coupling unit 18, instead of fingers 21, in combination with the coupling tube 29 and seal rings 33, 34 and 38, 39. Brief descriptions of variations of such gripping members are given below.

In a first variation, rotation of coupling tube 29 coaxially about an inner pipe section, such as section 52, draws a second coupling tube into itself through threaded engagement with it. The longitudinal travel of the second coupling draws one rim of a doughnut shaped rubber casing toward its mate, thus expanding the outer diameter of the rubber casing against the inner surface of the conventional pipe section, such as section 49, and the inner diameter of the rubber casing against the outer surface of the inner pipe section, such as section 52.

In another variation, a tapered rubber stopper is integrally fastened to the inner extending end of the coupling tube 29. The rubber stopper is provided with a hole which permits it to slide over the inner pipe section, but the tapered outer face of the rubber stopper is provided with a range of diameters such that, as it is forced into the conventional pipe section, the rubber stopper embraces the inner pipe section and pushes against the conventional pipe section. A multiplicity of longitudinal communicating tubes molded into the body of the rubber stopper provide for circulation of the fluid passing downwardly in the outer concentric passage 14.

Inflatable rubber members, in another variation, are attached to the inner extending end of the coupling tube. These rubber members are expanded by introducing air into them through an air pressure valve, of the type employed on automobile tires. The pressure exerted by the inflated rubber members is suflicient to develop the necessary frictional forces for action upon the outer wall surface of the inner pipe section and the inner wall surface of the conventional pipe section.

In another embodiment, a multiplicity of steel wedges are hingedly fastened to the inner extending end of the coupling tube. These wedges are tapered so that as they are forced into the annular space between the inner pipe section and the conventional pipe section, they develop the necessary frictional forces just before the limiting inserting distance of the inner pipe section into the conventional pipe section is reached. These wedges are faced with rubber or elastomer on their inner surfaces, and can be provided with limiting shoulders to exactly fix the amount of insertion of the inner pipe section into the conventional pipe section.

Permanent magnet wedging elements, in another embodiment, are moved longitudinally downwardly in nonmagnetic guides to positions where they fill the annular, or concentric space between the inner pipe section and the conventional pipe section. Each wedge has a shoulder at its outer top edge shaped to fit the bottom of the tool joint box of the conventional pipe section. The force of magnetic attraction developed by the wedges is designed to be sulficient to support the weight of the inner tube section.

In another variation, a multiplicity of pairs of wedging elements are uniformly spaced around the periphery of the inner extending end of the coupling tube. The inner halves of the wedging element pairs are fixed to the coupling tube and the outer halves of the element pairs are adapted to be movable. These outer, movable halves are threadedly connected to a ring, which upon being rotated, forces the outer Wedging element halves downwardly to generate the required frictional forces. The outward edge of the rotated ring is designed to bear against a shoulder ring which, in turn, is an integral part of the outer surface of the coupling tube.

A rotatable ring is used, in another variation, to set a multiplicity of slips, mounted in pairs. Rotation of the ring sets the paired slips bot-h against the inner pipe section and the conventional pipe section by urging a wedge downwardly between the pairs of slips.

In another variation, the coupling tube, at its inner extending end is cut by a multiplicity of longitudinal radial slots and is threadedly engaged by a tightening locking ring. The locking ring, upon being rotated, urges the inner surface of the coupling tube skirt against the outer surface of the inner pipe section. A multiplicity of shoulders formed integrally with the coupling tube, on its outer surface, engage the bottom of the tool joint box of the conventional pipe section.

In another embodiment, a multiplicity of shoulders on the outer surface of the coupling tube engage the bottom of the tool joint box of the conventional pipe section. To each shoulder a tapered arm is hingedly attached to extend downwardly. These arms are designed to provide a Wedging effect when forcibly introduced into the conventional pipe section. The arms, in this manner, develop suflicient frictional force to position the inner pipe section inside the conventional pipe section.

Obviously, many other modifications and variations of the present invention are possible in the light of the teachings given hereinabove. It is, therefore, to be understood that, within the scope of the appended claims, the invention can -be practiced otherwise than as specifically described. As used throughout with reference to mounting and inserting, the word reversibly is meant to define non-permanency or detachability. It should be clear from the foregoing that the preferred means shown on the drawing permits conversion from a standard single string to a dual string and yet the assembly may be readily dismantled whereby the single string may again be reused all without marking or damaging same. Further, in the preferred embodiment the individual fingers 21 are interchangeable, may be mass produced at a low cost and are of light weight.

With respect to actual practice of the invention, if desired and where necessary conventional spacers may be utilized throughout the drill string and between the coupling units to insure maintenance of the concentric relationship of the inner and outer pipe sections. Also, flange 32 of each coupling unit has been found useful as a locator when positioning the coupling units, such as on the upper end of section 12.

What is claimed is:

1. A method for changing from a single drill pipe section to a dual drill pipe section which comprises the steps of: introducing an inner drill pipe section into an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; reversibly locating a coupling means between the outer and inner pipe sections to seal the two fluid passages from each other and esta-bblish communication of the two respective fluid passages beyond the ends of the drill pipe sect-ions with corresponding fluid passages of adjoining drill pipe members; and firmly positioning the inner pipe section in the outer pipe section by generating positioning frictional forces upon the inside surface of the outer pipe section, the outside surface of the inner pipe section and adjacent surfaces of the coupling means.

2. A method for changing from a single drill pipe string to a dual drill pipe string which comprises the steps of: introducing an inner drill pipe section into an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; reversibly mounting a coupling means adjacent the upper end of the inner pipe section to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members; positioning the inner pipe section in the outer pipe section by generating positioning frictional forces upon the inside surface of the outer pipe section, the outside surface of the inner pipe section and adjacent surfaces of the coupling means to thus form a dual pipe section; introducing a second inner pipe section into a second outer pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; reversibly mounting a second coupling means adjacent the upper end of the second inner pipe section to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members; positioning the second inner pipe section in the second outer pipe section by generating positioning frictional forces upon the inside surface of the second outer pipe section, the outside surface of the second inner pipe section :and adjacent surfaces of the second coupling means to thus form a second dual pipe section; connecting the second outer pipe section to the upper end of the first mentioned outer pipe section to thereby connect the two dual pipe sections with the lower end of the second inner pipe section being in sealed fluid flow relationship with the first inner pipe section; and connecting additional dual pipe sections to complete the change from the single pipe string to a dual pipe string.

3. A method for changing from a single drill pipe string to a dual drill pipe string, according to claim 2, including the additional steps of: connecting the lower end of the first mentioned outer pipe section to a drill bit; connecting the lower end of the first mentioned inner pipe section to the drill bit; and forming communicating passages in the drill bit to establish communication between an annular passage inside the outer pipe sections and the passage inside the inner pipe sections.

4. Means for changing from a single drill pipe section to a dual drill pipe section which comprises: an inner drill pipe section disposed in an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; and coupling means reversibly mounted on the upper end of the inner pipe section, said coupling means being adapted for positioning concentrically the inner pipe section in the outer pipe section by the generation of positioning frictional forces upon the inside surface of the outer pipe section, the outside surface of the inner pipe section and adjacent surfaces of the coupling means to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members.

5. Means for changing from a single drill pipe string to a dual drill pipe string which comprises: an inner drill pipe section disposed in an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; coupling means reversibly located between the sections adjacent the upper end of the inner pipe section, said coupling means being adapted for positioning firmly and concentrically the inner pipe section in the outer pipe section by the generation of positioning frictional forces upon the inside surface of the outer pipe section, the outside surface of the inner pipe section and adjacent surfaces of the coupling means to thus form a dual pipe section to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members; a second inner pipe section disposed in a second outer pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; a second coupling means reversibly located between the upper end of the second inner and outer pipe sections,

said' second' coupling means being-substantially similar to said first coupling means and adapted for firmly and concentrically positioning the second inner pipe section in the second outer pipe section by the generation of positioning frictional forces upon the inside surface of the second outer pipe section, the outside surface of the second inner pipe section and adjacent surfaces of the second coupling means to thus form a second dual pipe section to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members; coupling means for connecting the second outer pipe section to the upper end of the first mentioned outer pipe section to thereby connect the two dual pipe sections with the lower end of the second iuner pipe section in sealed fluid flow relationship with the first inner pipe section; and additional dual pipe sections similar to the first and second dual pipe sections similarly coupled and connected throughout the dual pipe string.

6. Means for changing from a single drill pipe string to a dual drill pipe string according to claim 5, including a drill bit connected to the lower end of the first mentioned outer pipe section and in fluid flow relationship to the lower end of the first mentioned inner pipe section, said drill bit containing passages establishing communication between an annular passage inside the outer pipe sections and the passage inside the inner pipe sections.

7. Means for changing from a single drill pipe string to a dual drill pipe string according to claim 6, wherein each of said coupling means includes griping members adapted for gripping the inside surface and the, outside surface of an outer pipe section and an inner pipe section respectively in coupling engagement, a coupling tube connected to the gripping members and adapted for coupling two inner pipe sections end-to-end, and sealing means mounted on the coupling tube for sealing the coupled inner pipe sections against the entrance of fluid from the annular passage inside the outer pipe sections.

8. Means for changing from a single drill pipe string to a dual drill pipe string according to claim 6, wherein each of said coupling means includes elongate elastic gripping members adapted for gripping under compression the inside surface and the outside surface of an outer pipe section and an inner pipe section respectively in coupling engagement, a coupling tube connected to the gripping members and adapted for coupling two inner pipe sections end-to-end, and sealing means mounted on the coupling tube for sealing the coupled inner pipe sections against entrance of fluid from the anular passage inside the outer pipe sections.

'9. Means for changing from a single drill pipe section to a dual drill pipe section which comprises: an inner drill pipe section disposed in an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections; and coupling means reversibly located between the inner and outer pipe sections to seal the two fluid passages from each other and establish communication of the two respective fluid passages with correspond ing fluid passages of adjacent drill pipe members, said coupling means being adapted for positioning concentrically the inner pipe section in the outer pipe section by the generation of positioning forces upon the outer pipe section, the inner pipe section and the coupling means.

10. A method for'changing from a single drill pipe drilling section to a dual drill pipe drilling section comprising the steps of introducing an inner drill pipe section into an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer :and inner drill pipe sections, locating an expandable coupling unit between the sections to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members, and firmly positioning the inner section in the outer section by expanding the coupling unit.

11. A method for changing from a single drill pipe string to a dual drill pipe string comprising the steps of introducing an inner drill pipe section into an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections, locating an expandable coupling unit between the sections to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members, and firmly positioning the inner section in the outer section by expanding the coupling unit to form a first dual pipe section, similarly forming a second dual pipe section with a second coupling unit and a second inner and outer section, connecting the two dual pipe sections and forming and connecting additional dual pipe sections to complete the conversion of the single pipe string to a dual pipe string.

12. Means for changing from a single drill pipe section to a dual drill pipe section which comprises an inner drill pipe section disposed in an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections, an expandable coupling means between the sections to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members, and means for expanding said coupling means whereby the coupling means firmly positions the inner section in the outer section.

13. Means for changing from a single drill pipe string to a dual drill pipe string comprising an inner drill pipe section disposed in an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections, an expandable coupling means between the sections to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members, and said coupling means being expandable whereby the coupling means firmly positions the inner section in the outer section to form a first dual pipe section, a second inner pipe section disposed in a second outer pipe section to form a fluid passage inside the inner drill pipe section and an annular fluid passage between the outer and inner drill pipe sections, a second expandable coupling means between the second inner and and outer sections to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members, said second coupling means being expandable whereby a second dual pipe section is formed, said first and second dual pipe sections being connectable, and additional similar dual pipe sections being connectable throughout the dual pipe string.

14. Means for changing from a single drill pipe section to a dual drill pipe section which comprises an inner drill pipe section disposed in an outer drill pipe section to form a fluid passage inside the inner drill pipe section and an annular passage between the outer and inner drill pipe sections, a coupling unit between the sections capable of generating forces to firmly and concentrically position the sections and means for causing said coupling unit to generate such forces and to seal the two fluid passages from each other and establish communication of the two respective fluid passages with corresponding fluid passages of adjacent drill pipe members.

References Cited by the Examiner UNITED STATES PATENTS 1,547,461 7/1925 Steele -215 X 1,862,260 6/1932 Edmunds 175215 X 1,876,627 9/1932 Davis et a1. 175-21 1,991,455 2/1935 Gottwald 138113 2,054,859 9/1936 Kitching 285-433 2,186,139 1/1940 Hild 285144 X 2,657,016 10/1953 Grable 175215 2,706,495 4/1955 Risley 285138 X 2,915,089 12/1959 Horsting 138-1l3 CHARLES E. OCONNELL, Primary Examiner.

R. E. FAVREAU, Assistant Examiner. 

10. A METHOD FOR CHANGING FROM A SINGLE DRILL PIPE DRILLING SECTION TO A DUAL DRILL PIPE DRILLING SECTION COMPRISING THE STEPS OF INTRODUCING AN INNER DRILL PIPE SECTION INTO AN OUTER DRILL PIPE SECTION TO FORM A FLUID PASSAGE INSIDE THE INNER DRILL PIPE SECTION AND AN ANNULAR FLUID PASSAGE BETWEEN THE OUTER AND INNER DRILL PIPE SECTIONS, LOCATING AND EXPANDABLE COUPLING UNIT BETWEEN THE SECTIONS TO SEAL THE TWO FLUID PASSAGES FROM EACH OTHER AND ESTABLISH COMMUNICATION OF THE TWO RESPECTIVE FLUID PASSAGES WITH CORRESPONDING FLUID PASSAGES OF ADJACENT DRILL PIPE MEMBERS, AND FIRMLY POSITIONING THE INNER SECTION IN THE OUTER SECTION BY EXPANDING THE COUPLING UNIT. 